The present invention relates to the diagnosis and treatment of partial or complete upper airway occlusion, a condition where the upper airway collapses, particularly under the reduced pressure generated by inhalation. This is most likely to happen during unconsciousness, sleep or anaesthesia.
A particular application of the present invention is to the diagnosis and/or treatment of snoring and sleep apnea. Sleep apnea is characterized by complete occlusion of the upper airway passage during sleep while snoring is characterized by partial occlusion. Obstructive sleep apnea sufferers repeatedly choke on their tongue and soft palate throughout an entire sleep period resulting in lowered arterial blood oxygen levels and poor quality of sleep. It should be realized that although the following specification discusses sleep apnea in detail, the present invention also applies to the diagnosis and treatment of other forms of upper airway disorders.
Reference to international patent publication WO 82/03548 will show that the application of continuous positive airway pressure (CPAP) has been used as a means of treating the occurrence of obstructive sleep apnea. The patient is connected to a positive pressure air supply by means of a nose mask or nasal prongs. The air supply breathed by the patient, is at all times, at slightly greater than atmospheric pressure. For example, gauge pressures will typically be within the range of 2 cm to 25 cm. It has been found that the application of continuous positive airway pressure provides what can be described as a xe2x80x9cpneumatic splintxe2x80x9d, supporting and stabilizing the upper airway and thus eliminating the occurrence of upper airway occlusions. It is effective in eliminating both snoring and obstructive sleep apnea and in many cases, is effective in treating central and mixed apnea.
The airway pressure required for effective CPAP therapy differs from patient to patient. In order to discover the airway pressure which is most effective for a particular individual, the practice has been for the patient to undergo two sleep studies at an appropriate observation facility such as a hospital, clinic or laboratory. The first night is spent observing the patient in sleep and recording selected parameters such as oxygen saturation, chest wall and abdominal movement, air flow, expired CO2, ECG, EEG, EMG and eye movement. This information can be interpreted to diagnose the nature of the sleeping disorder and confirm the presence or absence of apnea and where present, the frequency and duration of apneic episodes and extent and duration of associated oxygen desaturation. Apneas can be identified as obstructive, central or mixed. The second night is spent with the patient undergoing nasal CPAP therapy. When apnea is observed the CPAP setting is increased to prevent the apnea. The pressure setting at the end of the sleep period, i.e., the maximum used, is deemed to be the appropriate setting for that patient. For a given patient in a given physical condition there will be found different minimum pressures for various stages of sleep in order to prevent occlusions. Furthermore, these various pressures will, in fact, vary from day to day depending upon the patient""s physical condition, for example, nasal congestion, general tiredness, effects of drugs such as alcohol, as well as their sleeping posture. Thus the appropriate pressure found in the laboratory is necessarily the maximum of all -these minimum pressures for that particular night and is not necessarily the ideal pressure for all occasions nor for every night. It will generally be higher than necessary for most of the night.
Also patients must be able to operate a CPAP system to deliver appropriate airway pressure at their home where their general physical condition or state of health may be quite different to that in the sleep clinic, and will certainly vary from day to day. The patient""s physical condition often improves due to CPAP therapy. It is often the case that after a period of therapy the necessary airway pressure can be reduced by some amount while still preventing the occurrence of obstructive sleep apnea. However, the prior art provides no facility to take advantage of this fact other than by regular diagnostic sleep periods in a sleep clinic or hospital.
The long term effects of CPAP therapy are unknown so it is desirable to keep the airway pressure as low as practicable, particularly if a patient requires long term treatment. Lower airway pressures also result in a lower face mask pressure which is generally more comfortable for the patient. It has been found that CPAP induces patients to swallow and this inducement to swallow can be reduced by lowering the airway pressure. Thus it is desirable to use the lowest practicable airway pressure that is effective in preventing airway occlusion during CPAP therapy for the comfort and, possibly, the long term safety of the patient. Also, a lower airway pressure requires less energy consumption and a less complex and therefore less expensive apparatus which is generally quieter.
Low airway pressures are also desirable before and during the early stage of each sleep period as the increased comfort of an initially lower airway pressure allows the patient to more easily fall asleep. When a patient undergoing CPAP opens his mouth with pressurized air being forced through the nose the pressured air exits out of the mouth producing an unpleasant sensation. This can occur when the patient puts on the mask connected to the pressured air supply before falling asleep and some patients will therefore leave the mask off for as long as possible and may in fact fall asleep without wearing the mask and therefore without the benefits of the CPAP therapy.
Presently available CPAP units do hot address this problem and so there is a need to provide a CPAP device which will be more acceptable to the patient before and during initial sleep by operating at an initially low pressure but automatically increasing to an appropriate therapeutic pressure before apnea occurs.
In addition to the problems associated with administering CPAP therapy there exists the inconvenience and cost of diagnosis which is currently undertaken by overnight observation at a sleep clinic or the like. Hence a simple means whereby a patient""s apnea problem can be diagnosed at home without supervision is clearly desirable as well as a CPAP device which will deliver a continuously minimum appropriate pressure for substantially the entire period of therapy.
Devices are available to detect apnea. For example, International Patent publication WO/86/05965 discloses an apparatus which includes acoustic respiration sensors, background sound sensors and movement sensors. Such apparatus are capable of detecting breathing sounds, comparing those sounds with body movements and background noises and by further comparing the results with a data base of information, to indicate whether the patient is undergoing a normal or abnormal breathing pattern. Such apparatus can sound an alarm on the occurrence of apnea.
Another device which could be readily adapted to detect and record the occurrence of apneic episodes is disclosed in U.S. Pat. No. 4,537,190. That apparatus is responsive to the CO2 levels in exhaled air during respiration and is also responsive to the absence of respiration (i.e., apnea) in which case it can switch on a ventilator.
These devices are deficient in that they do not take advantage of the indication of apnea obtained exclusively from a recording from a single sound transducer (microphone) preferably located in the CPAP nose mask or prongs that can be interpreted by a skilled physician. The sound transducer, in its most general form, consists of a pressure transducer which, in addition to detecting snoring sounds, can detect other respiratory parameters such as the rate of breathing, inhaled air flow or inhaled air flow rate. The inherent simplicity of this form of measurement makes it safe and practicable for anybody to use in their own home with a minimum of prior instruction.
Although diagnosis in a sleep clinic as outlined above is beneficial, it has some deficiencies. A patient is likely not to sleep in a fully relaxed state in an unfamiliar environment and a single night is insufficient to obtain a pressure setting that will be optimal in the long run. Thus home therapy at the pressure setting arrived at in this way is likely to be less than 100% effective on some occasions and higher than necessary for a substantial portion of the time. The cost and inconvenience of a sleep study in a hospital setting are to be avoided if possible.
A skilled physician can usually recognize the symptoms of sleep apnea from questioning and examining a patient. Where no other indications are present there is very little risk in attempting nasal CPAP therapy without further testing as the treatment is fail safe and non-invasive. However, a very useful intermediate step would be to analyze the pattern of respiratory sounds over one or more full nights of sleep. Interpretation of these patterns together with questioning and examination will, in many cases, provide sufficient confirmation of apnea to prescribe nasal CPAP therapy. If nasal CPAP eliminates the symptoms of day time sleepiness (as assessed by the patient) and of apneic snoring patterns (as assessed by analysis of recorded respiratory sounds while on nasal CPAP), the treatment can be continued. Further check ups can be conducted at intervals recommended by the physician.
In the most general form of the device, the intermediate step before attempting nasal CPAP therapy would be to analyse the patterns of the respiratory parameters that can be obtained from a single pressure transducer. These parameters include, in addition to acoustic rate of breathing, inhaled/exhaled air volume and inhaled/exhaled air flow rate, and provide comprehensive information for the physician to assess the patient""s condition. This additional information, coming from the same pressure transducer, is available at marginal additional cost to the acoustic recording and with no additional complexity in home use by the patient.
The measurement of other parameters would provide further information to assist diagnoses and the acoustic and/or other respiratory recordings described above can readily be used in conjunction with other monitors such as ECG and/or pulse oximetry. Suitable monitors are available to measure both these parameters in the home but with increased information comes much higher cost of equipment and increase complexity in using the equipment. The correlation between reduced oxygen saturation and apnea is sufficiently well established to infer oxygen desaturation from the confirmation of an apneic event.
Diagnoses which are not conclusive from examination and home monitoring will continue to be confirmed from full sleep studies in a Sleep Disorders Center.
Thus the prior art monitors and methods are deficient at least in that the resulting therapy is not 100% effective at all times, it is delivered at higher pressure than necessary for substantial periods, the equipment is expensive and has required diagnosis in specialized clinics.
The present inventors have recognized the detection of the noise of snoring or more particularly snoring patterns as a reliable parameter for detecting apneas as well as the imminent onset of apneic episodes. Characteristic snoring patterns can be associated with various sleep conditions including apnea and in fact in most (perhaps 95%) of sleep apnea sufferers, distinctive snoring patterns closely precede apneic episodes as will be later discussed. Characteristic patterns of other respiratory parameters such as rate of breathing, inhaled/exhaled air volume and inhaled/exhaled air flow rate, obtainable from the same pressure transducer as snoring patterns, can also be used for detecting apneas as well as the imminent onset of apneic episodes. Any one parameter or combination of parameters may be used for detecting apneas or other breathing disorders, as well as the imminent onset of apneas or other breathing disorders.
A pressure transducer such as a microphone is a suitable detector of these characteristic snoring sounds, and in particular the sounds of snoring patterns. Furthermore, the quality of the sounds monitored can be enhanced by placing the microphone within an enclosure which is in sound communication with a patient""s respiratory system. By enclosing the microphone, a physical noise barrier isolates the microphone from external sounds. If the enclosure is in sound communication with the patient""s respiratory system the natural stethoscope effect of the patient""s respiratory system is thereby exploited. A further benefit of such a device is that the microphone is not in direct contact with any part of the patient""s body. Thus, relative movement between the microphone and the patient""s body, which is a noise source as far as monitoring is concerned, can be avoided.
Monitoring of a patient""s snoring patterns alone can in many instances provide information indicative of his/her condition, whether he/she suffers mild, medium or extreme apneic episodes, how often the episodes occur and therefore whether CPAP therapy will be beneficial. A snoring monitor can accordingly be used at least as a preliminary diagnostic tool with or without monitoring other physiological parameters to provide information on the frequency and severity of snoring, hypopnea and apnea in a patient. Its simplicity and inexpensive nature allows it to be used at home in the patient""s usual environment without the expense of a night in a sleep clinic. In some cases, e.g., where unusual snoring patterns are encountered, the diagnosis of the data from the snoring monitor will not be conclusive and the traditional full diagnosis in a sleep clinic will be required.
Thus, in one form of this invention there is provided a diagnostic device comprising a nose piece substantially fluidly sealable to the nasal air passages of a patient, a sound transducer in sound communication with the interior of the nose piece so as to be, when in use, in sound communication with the respiratory system of the patient and to detect and produce a signal responsive to the sounds of patient snoring, and recording equipment associated with the sound transducer for recording information indicative of the signal.
In another form of the diagnostic device, there is provided a nose piece substantially fluidly sealable to, or in sealed fluid communication with, the nasal air passages of a patient, a pressure transducer in pressure communication with the interior of the nose piece so as to be in pressure communication with the respiratory system of the patient and to detect and produce a signal or signals responsive to snoring and other respiratory parameters, such as rate of breathing, inhaled/exhaled air volume and inhaled/exhaled air flow rate, of the patient, and recording equipment associated with the pressure transducer for recording information indicative of one or more of the signals.
In one preferred embodiment of the diagnostic device, the intensity of the signal is recorded with respect to time. In another embodiment of the diagnostic device the microphone output is fed through an amplifier or filter to differentiate normal breathing sounds from those indicative of snoring, and the intensities and time pattern of the differentiated sounds are recorded. Further, in a embodiment of the diagnostic device the frequency and duration of airway occlusions are calculated by preprogrammed processing of the detected signal, the processed signal is recorded as a time chart or a table interpreted by the physician.
In another embodiment of the diagnostic device, the pressure transducer measures or detects a number of audio or low frequency waves generated within the mask during breathing including a high frequency audio wave produced by the air flow into the mask and by the rotating elements of the air source, a low frequency audio wave produced by the resonance of the airways or chest cavity during snoring, a very low frequency large amplitude wave corresponding to the pressure variations produced by the air flowing over a section of the nose piece, which may include a flow restrictor to amplify the pressure drop. After suitable amplification, the output signal from the pressure transducer passes through filtering and conditioning circuits to separate the different waves of interest, including the low frequency audio wave described above and the very low frequency pressure wave produced by the air flowing over the said section of the nose piece.
The breathing rate or interruption of breathing, the air flow rate during inhalation/exhalation and the beginning/end points of the breathing cycle are derived from the very low frequency pressure wave after further. sampling or processing. Using a suitable integration technique, the air flow is integrated for the duration of the inspiration and/or expiration phase using the said beginning/end points. This integral of air flow corresponds to the inhaled/exhaled air volume for each breath. The processed signals are recorded as a time chart or a table interpreted by a physician.
Thus in a number of cases such a snoring monitor provides an effective substitute for the traditional first night in the sleep clinic. The monitor in its more general form provides information on respiratory parameters such as rate of breathing, inhaled/exhaled air volume, and inhaled/exhaled air flow rate, as well as snoring. Where diagnosis indicates CPAP therapy to be appropriate the patient can go straight to the traditional second night at the sleep clinic so as to determine their appropriate CPAP setting for their condition, or they could commence use of an automatic CPAP device such as the unit described hereunder.
The monitoring of snoring patterns is useful not only for recording information regarding those patterns for diagnostic purposes but is also useful in that certain snoring patterns are a precursor to most apneic episodes in a large proportion of sleep apnea victims. Thus, an effective CPAP device can be controlled by a feedback system in which snoring patterns are monitored and CPAP pressure is raised at the detection of predefined snoring patterns so as to provide increased airway pressure before, and in fact generally prevent the occurrence of, apneic episodes.
Thus, in another form of the invention there is provided in a CPAP apparatus a feedback control comprising a sound monitoring device in sound communication with the respiratory system of a patient when using the apparatus, and a processor responsive to output from the sound monitoring device so as to control CPAP pressure according to patient requirements as determined by output from the sound monitoring device in order to prevent apneic episodes.
The monitoring of other respiratory parameters, as well as snoring, is also useful not only for recording those patterns for diagnostic purposes but is also useful in that certain patterns of these parameters are a precursor to most apneic episodes and other forms of breathing disorders that can be treated by nasal CPAP. Thus an effective CPAP device can be controlled by a feedback system in which patterns of respiratory parameters are monitored and CPAP pressure is raised at the detection of pre-defined patterns so as to provide increased airway pressure, before and in fact generally prevent the occurrence of apneic episodes or other forms of breathing disorders.
For example, the air flow rate inhaled or exhaled by the patient is compared to a base line level for that patient and if the flow rate is lower than the base line, the CPAP pressure is raised. Alternatively, the time interval between the onset of each inspiration or expiration is compared to a base line level for that patient and if the interval is greater than the base line, the CPAP pressure is raised. Alternatively, the integrated inhaled or exhaled volume of air is averaged over a relatively large number of breaths to give a moving base line for the patient. Simultaneously, the integrated inhaled or exhaled volume of air is averaged over a short time interval. If the volume over the short time interval is less than the volume over the relatively large number of breaths by a specified amount, CPAP pressure is raised.
Preferably, the feedback control is co-operative with a variable speed air compressor of the CPAP apparatus, the processor regulating the speed of the compressor when in use by increasing speed in response to a said signal equivalent to a preprogrammed signal indicative of a predetermined snoring pattern. The said signal could also be indicative of a predetermined pattern in other respiratory parameters.
Preferably, the control system furthermore decreases speed of the air compressor in the absence of the signal after a period of time in accordance with the predefined procedure.
In another form of the feedback device of the invention there is provided a CPAP apparatus including a variable speed air compressor, a nose piece for sealed air communication with a patient""s respiratory system, an air line from the compressor to the nose piece, an enclosed microphone connected to the air line so as to be in sound communication with the patient""s respiratory system, and a feedback system controlling the speed of the air compressor in response to an output from the microphone so as to increase compressor speed in response to detected sound indicative of heavy snoring in accordance with a pre-defined procedure. Preferably, the feedback system reduces the speed of the air compressor in response to an absence of the said sound in accordance with the predefined procedure.
In another form of the apparatus there is provided a CPAP apparatus including a variable speed air compressor, a nose piece for sealed air communication with a patient""s respiratory system, an air line from the compressor to the nose piece, a pressure transducer connected to the air line so as to be in pressure communication with the patient""s respiratory system, and a feedback system controlling the speed of the air compressor in response to an output or outputs from the pressure transducer so as to increase compressor speed in response to detected patterns of sound or respiratory parameters indicative of snoring or breathing disorders in accordance with a predefined procedure. Preferably the feedback system reduces the speed of the air compressor in response to an absence of the said patterns of sound or respiratory parameters in accordance with the predefined procedures.
Disadvantages in the prior art are also ameliorated by a further aspect of the invention which provides a variable speed air compressor and control system in the CPAP apparatus, the control system regulating the speed of the compressor when in use by increasing its speed in accordance with a predefined procedure whereby the commencement of operation of the compressor occurs at a preselected minimum speed with a gradually increasing compressor speed over a preselected period of time to a preselected maximum speed.
This embodiment of the invention provides an advantage in that the patient is exposed to a comfortably low pressure before falling asleep and during initial stages of sleep while the necessary therapeutic pressure is reached by the time it is required.